Lava lake surface characterization by thermal imaging: Erta 'Ale volcano (Ethiopia)

Active lava lakes represent the exposed, uppermost part of convecting magma systems and provide
windows into the dynamics of magma transport and degassing. Erta ’Ale volcano located within the
Danakil Depression in Ethiopia hosts one of the few permanent convecting lava lakes, probably active for a
century or more. We report here on the main features of the lava lake surface based on observations from
an infrared thermal camera made on 11 November 2006. Efficient magma circulation was reflected in the
sustained transport of the surface, which was composed of pronounced incandescent cracks that separated
wide plates of cooler crust. These crossed the lake from the upwelling to the downwelling margin with
mean speeds ranging between 0.01 and 0.15 m s 1. Hot spots eventually opened in the middle of crust
plates and/or along cracks. These produced mild explosive activity lasting commonly between 10 and
200 s. Apparent temperatures of cracks ranged between 700 and 1070 C, and of crust between 300
and 500 C. Radiant power output of the lake varied between 45 and 76 MWaccording to the superficial
activity and continuous resurfacing of the lake. Time series analysis of the radiant power output data
reveals cyclicity with a period of 10 min. The combination of visual and thermal observations with
apparent mean temperatures and convection rates allows us to interpret these signals as the periodic release
of hot overpressured gas bubbles at the lake surface.

The project ‘‘Sviluppo di sistemi di monitoraggio’’ (Dipartimento di Protezione Civile di Regione Sicilia, INGV Catania Section, Italy), the Leverhulme Trust, the BBC, and the Ethiopian Air Force.

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